Mixing 2 buffers at 2 different pH

[MestizoJoe]

If you have two buffers, lets say 50mM Phosphate at pH 2.1 and 50mM acetate at pH 4.8, can you mix the two in a 1:1 ratio to achieve a buffer at the new pH?

I know that each buffer has its respective pH range, but I've never seen anyone write about combinations and what happens to buffer capacity in those conditions. Maybe the answer is an obvious no, but it doesn't seem so obvious to me.

The reason I ask is because if the answer is yes, it can make optimization a bit easier.

[Uwe Neue]

It will not be a buffer - you will be outside the typical ranges of suitable buffer capacity for both. Use a buffer with an intermediate pKa, for example a formic acid buffer.

[pelle-plutt]

Well, technically it's still a buffer.
By mixing the two buffers you would get a buffer solution with a pH somewhere between 2.1 and 4.8. The buffer capacity is rather low compared to the parent solutions but at 50 mM it might still be high enough for your application. As always, it depends on what you want to use it for.

During my university studies I knew how to calculate the buffer capacity of buffer solutions (and mixtures) but it's all forgotten now.

[HW Mueller]

So we either forgot how to do it or are too lazy to calculate the pH of the proposed mixture (the pH would be necessary to calc the buffer capacity, all very tedious). The gut feeling, though, tells me that Uwe is close.
Note also that the addition of 1:1 will half the concentration of the components.

[Uwe Neue]

You can find pictures of peak capacity in the following publication: U. D. Neue, A. Méndez, K. Tran, D. M. Diehl, “pH and Selectivity in Reversed-Phase Chromatographyâ€